This invention relates generally to plastic lens compositions and methods and apparatus for making plastic lenses, and in one of its aspects to corrective or plane plastic lenses for use in eyeglasses and the like.
Optical lenses have been produced from the polymer of diethylene glycol bis(allyl)-carbonate (DEG-BAC) by thermal curing techniques. These techniques for polymerizing DEG-BAC to produce an optical lens, however, have several disadvantages and drawbacks. One of the most significant drawbacks is that it takes approximately 12 hours to produce a lens according to this technique and therefore a lens forming mold can produce at most two lenses per day.
Moreover, the thermal curing process employs a thermal catalyst so that the polymerizable mixture of DEG-BAC and catalyst will slowly polymerize even while refrigerated. The polymerizable mixture therefore has a very short shelf life and must be used within a short time or it will harden in its container.
Furthermore, the thermal catalysts utilized in these procedures are quite volatile and dangerous to work with requiring extreme care in handling.
U.S. Pat. No. 4,166,088 discloses the formation of a plastic lens by disposing a lens forming material comprising a liquid monomer and a photosensitive initiator into a mold cavity defined in part between a pair of spaced apart molds each having a lens forming surface facing the cavity and an outer opposed surface, and then directing rays of ultraviolet light against the outer surface of at least one of the molds to act on the lens forming material in the cavity to produce a lens therefrom.
U.S. Pat. Nos. 3,038,210 and 3,222,432 disclose the heating of a lens forming material in a mold cavity by an external heat source.
U.S. Pat. No. 4,298,005 discloses an apparatus for generating ultraviolet light having a wavelength in the range of 320 to 450 nm for hardening plastics.
The polymer of DEG-BAC exhibits desirable optical and mechanical properties. These properties include high light transmission, high clarity, and high index of refraction together with high abrasion and impact resistance. These properties in the past made DEG-BAC one of the leading monomers in the manufacture of high quality lenses, face shields, sun and safety glasses. Other properties of DEG-BAC, however, such as its slow rate of polymerization make it an undesirable monomer in the manufacture of these items.
One aspect of the present invention is to provide a method and apparatus for making a plastic lens, such as an optical lens for use in eyeglasses and the like.
Another aspect of the present invention is to reduce the yellowing of the plastic lens during the making thereof.
Yellowing of the plastic lens has been found to be dependent upon the identity of the components utilized to form the lens forming material.
According to one embodiment of the present invention, a lens forming composition comprises diethylene glycol bis(allyl carbonate) (DEG-BAC) and one or more mono or multifunctional acrylate monomers that can be radiation cured to produce a hard, tough, clear, and strain-free polymeric material which has excellent optical qualities. The composition further comprises a suitable photoinitiator that is selected preferably from the group consisting of 2-hydroxy-2-methyl-1-phenyl-propan-1-one and 1-hydroxy-cyclohexyl phenyl ketone. Preferably, the mono or multifunctional acrylate monomers of this composition may be selected from tetrahydrofurfuryl acrylate (TFFA), trimethylol propane triacrylate (TMPTA) and tetrahydrofurfuryl-methacrylate (TFFMA)
It is a further object of the present invention to provide a plastic lens that can be produced in less than two hours and preferably in Less than one hour.
It is a still further object of the present invention to provide a plastic lens that has no distortions, cracks, patterns, striations, defects, or aberrations.
It is a still further object of the present invention to provide a plastic lens that is hard, strong and durable, and has very little flexibility at high temperatures.
It is a still further object of the present invention to provide a plastic lens that easily releases from the molding apparatus.
Toward the fulfillment of the above and other objects, according to another embodiment of the present invention, a lens forming composition comprises aromatic-containing bis(allyl carbonate)-functional monomer and at least one polyethylenic-functional monomer containing two ethylenically unsaturated groups selected from acrylyl and methacrylyl. The composition further comprises a suitable photoinitiator and optionally compresses one or more of a polyethylenic-functional monomer containing three ethylenically unsaturated groups selected from acrylyl and methacrylyl, styrene, a mold release agent and a dye.
According to a further embodiment of the present invention, a lens forming composition comprises at least one polyethylenic-functional monomer containing two ethylenically unsaturated groups selected from acrylyl and methacrylyl. The composition further comprises a suitable photoinitiator and optionally comprises one or more of a polyethylenic-functional monomer containing three ethylenically unsaturated groups selected from acrylyl and methacrylyl, styrene, a mold release agent and a dye.
According to a still further embodiment of the present invention, a lens forming composition comprises a polyethylenic-functional monomer containing three ethylenically unsaturated groups selected from acrylyl and methacrylyl. The composition further comprises a suitable photoinitiator and optionally comprises one or more of an aromatic-containing bis(allyl carbonate)-functional monomer, styrene, a mold release agent and a dye.